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As a top U.S. climate scientist attributed the country’s record heat waves and drought definitively to climate change, the National Oceanic and Atmospheric Administration (NOAA) called July the hottest month on record since we started keeping track.

No other explanation is possible for events ranging from last year’s Texas drought and the 2010 heat wave in Russia, said James Hansen, who directs the Goddard Institute for Space Studies at the U.S. National Aeronautics and Space Administration (NASA), in an interview with Bloomberg.

Hansen, who has been pushing to reduce carbon dioxide emissions for decades, believes so strongly in his message that he was arrested outside the White House last year protesting the Keystone XL pipeline, as were many from Indian country. Tapping the Alberta oil sands for such a project, he warned the Obama Administration, would be “game over” for Mother Earth’s climate.

More telling for Hansen was that the paper he wrote with two co-authors, researched and compiled before this year’s record drought and heat hit, lays out the pattern that these events fit into, Bloomberg said. Since the paper was written, the U.S. Drought Monitor has said that two thirds of the U.S. is gripped in drought, the worst since the 1950s, and an epidemic of wildfires has scorched more than 2 million acres.

The heat didn’t begin with summer, the experts pointed out. A lack of snow and cold over the winter paved the way for a sizzling summer, with January through June being the warmest on record in the U.S., according to the National Weather Service. Average temperatures were 4.5 degrees higher than the average over the 20th century, and 28 states posted record warmth.

The first five days of January 2012 alone saw the breaking of 799 daytime heat records, said Jake Crouch, a climate scientist from the NOAA National Climatic Data Center.

"Last year's was the fourth warmest winter since 1895,” he said in an August 3 statement from NASA. “And it was dry, with a dearth of snowfall in many places. During most of this past winter and spring, a positive North Atlantic Oscillation pressure pattern kept the jet stream further north and the U.S. warmer and drier than normal."

This left little moisture in the soil, which meant that the sun’s energy and radiation got converted to heat rather than dissipated, he said.

In July the average temperature for the contiguous U.S. was 77.6°F, 3.3°F above average for the 20th century, NOAA scientists said in their statement. It made for the hottest July and the hottest month on record for the U.S. and created the warmest 12-month period recorded since temperatures were first logged in 1895. The previous record was in July 1936, when average U.S. temperatures reached 77.4°F, NOAA said.

Although July precipitation totaled just 0.19 inch below average, at 2.57 inches, the middle of the U.S. was subject to dryness that came close to breaking records, and by the end of the month, the U.S. Drought Monitor had announced a “drought footprint” covering nearly 63 percent of the lower 48 states, NOAA said.

Some experts, like Hansen, said global warming must be to blame, especially given the plethora of greenhouse gases now present in the atmosphere, many of them from human activity.

"CO2 is up from 280 parts per million in the 19th century atmosphere to almost 400 parts per million now—a 43% increase," said NASA climatologist Bill Patzert in the agency’s statement. "We're emitting six times more carbon from fossil fuel use now than we did 50 years ago. Atmospheric CO2 hasn't been this high in 400,000 years."

Other NASA scientists, while not doubting that the world is heating up, said that extreme weather is cyclical.

"The central US suffered several heat waves in the 1930s—the dust bowl years—when more statewide, all-time record high temperatures were set than in any other decade,” said John Christy, a scientist from the University of Alabama in Huntsville, in NASA’s statement. “And the western U.S. experienced decades-long droughts in the 12th century. So dry were mountain areas that we can still see near-hundred-year-old trees standing upright in the bottom of alpine lakes where they grew on dry ground 900 years ago. This shows that in the 12th century it was so dry and hot that the lakes dried up and allowed trees to grow over a significant period before moisture finally returned."

This video illustrates the temperatures and the debate.

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